Coloring of oxide-coated aluminum



United States Patent Ofiice 3,1il3fi2ii Patented Oct. 22, 1963 3,108,026COLORENG F OXIDE-COATED ALUMINUM Rolf Dessauer, Braudywine Hundred, DeL,assignor to E. i. du Pont de Nernours and Company, Wilmington, Del., acorporation of Delaware No Drawing. Filed Oct. 10, 1960, Ser. No.

8 Claims. ((11. 148-61) This invention relates to colored aluminum andmore particularly to a process of coloring oxide-coated alurninum so asto impart a light-fast green-yellow color thereto.

This application is a continuation-in-part of my copending applicationSerial No. 768,051, filed October 20, 1958, now abandoned.

The coloring of aluminum is old in the art. In one process the aluminumis anodized making it dye receptive and the anodized aluminum is thentreated in an aqueous dyeing process with an organic dye containingsulfonic or carboxylic acid groups. In a more recent process forcoloring anodized aluminum a printing technique is used. This is a morerapid process and has greater flexibility. For example, printing may beaccomplished with several colors simultaneously by using appropriateprinting rolls. In this printing technique the coloring agents arepreferably applied from a nonaqueous vehicle and thus, colorants arerequired which have solubility or dispersibility in a non-aqueousvehicle. One of the difiiculties encountered in this desirable printingprocess is that no coloring agents are available which are soluble ordispersible in a non-aqueous vehicle and which impart a light-fastgreen-yellow color to the alu minum.

It is an object of the present invention to provide 4 oxide-coatedaluminum having a lightfast, green-yellow color. A further object is toprovide a process for imparting a light-fast, grcen-yellow color toanodized aluminum by means of a printing technique. Other objects willappear hereinafter.

These and other objects of this invention are accomplished by a processof coloring oxide-coated aluminum with a non-aqueous ink which comprisesimparting a green-yellow color to the aluminum by using as the coloringagent an o-hydroxybenzophenone of the formula R OH | 0 I ll 3 X OX l I YY wherein R is hydrogen or hydroxy, X is hydrogen, hydroxy or a loweralkoxy radical, X is hydrogen or a lower alkyl radical, Y is hydrogen, atertiary lower alkyl radical or acyl radical, R'CO-, wherein R is alower alkyl radical or a phenyl radical, with the proviso that Y neednot necessarily be the same in each occurrence. The process of thepresent invention consists in the use of the o-hydroxybenzophenone asthe coloring agent in the coloring of oxide-coated aluminum whereby agreenyellow color is imparted to the aluminum.

The process of printing anodized aluminum with a nonaqueous printingvehicle is well known in the art. In

general this process comprises the steps of printing on an anodizedaluminum surface with an ink comprising a dye dissolved or dispersed ina film-forming vehicle and then sealing the color on the surface bytreating with boiling water.

In one method of carrying out this invention the coloring agent, i.e.,the o-hydroxybenzophenone, is dispersed in an inert vehicle and thedispersion is printed with conventional oil-set printing equipment .ontooxide-coated aluminum. Any conventional vehicle may be used which isinert to the coloring agent and the aluminum. Representative vehiclesinclude a varnish, linseed oil and nitrocellulose dissolved in methylbutyl ketone. The printed article is subsequently heated at temperaturesof C. to C. for about 15 to 30 minutes to bond the coloring agent to thesubstrate. Then the aluminum is immersed in an aqueous bath in which itis heated at the boil for about 15 minutes or longer. This treatmentserves to seal the oxide-coated aluminum surface. Any unreacted ink isthen removed by a solvent wash. Representative solvents which may 'beused for this wash include alcohols, lower ketones, etc.

If desired, the coloring agent may be dissolved in a solvent, such asdimethylformamide, butanol, Z-methoxy (or ethoxy) ethanol, etc. and thenprinted onto the oxidecoated aluminum. In lieu of printing saidsolutions of the hyd-roxybenzophenones onto said aluminum, they may beapplied by well-known spraying, dipping or painting techniques to obtainsolid colorations. For this purpose one may employ mixtures of theabove-named solvents, or these solvents which are diluted with loweralcohols or lower ketones.

The coloring agents which may be used in the present invention to imparta green-yellow color to the oxidecoated aluminum are selected from theclass of ohydroxybenzophenones described above. Representative compoundsinclude 2,4-dihydroxyrbenzophenone; S-tert.ibutyl-2,4-dihydroxybenzophenone; 2,2',4 trihydroxybenzophenone;5-tert.butyl 2,2,4 trihydroxybenzophenone;2,2-dihydroxy-4-rnethoxybenzophenone; 2,2 dihydroxy- 4butoxybenzophenone; 2,2,4,4'-tetrahydroxybenzophenone;5,S-di-tert.1butyl 2,2',4,4 tetrahydroxybenzophenone; 2,2 dihydroxy 4,4di-methoxy'benzophenone; 5,5-di-tert.butyl 2,2dihydroxy-4,4-dimethoxybenzophenone; 2,2'-dihydroxy 4methoxy-4-ethoxybenzophenone; 2,2,4-trihydroxy 5 (/3-methylheptyD-benzophenone; 4,6-dibenzoyl resorcinol; 4,6-diacetyl resorcinol.These o-hydroxybenzophenones are either colorless or essentiallycolorless compounds and it is, therefore, quite surprising that whenused in a process for coloring oxidecoate-d aluminum, they impart agreen-yellow color to the aluminum. The color imparted to the aluminumas a result of using these compounds has excellent light 'fastness.

The green-yellow color imparted to the oxide-coated aluminum is believedto be due to a chemical combination between the coloring agent and thealuminum oxide surface, and this chemical combination causes abathochromic shift in the hue of the colorant. It appears that theoxide-coated aluminum contains on its surface an aluminum chelate of theo-hydroxybenzophenone. The green-yellow colored =oxide-coated aluminumhas a wide variety of uses such as in automobile trim, printed signs,drinking tumblers, and interior and exterior decorations.

The following examples will better illustrate the nature of the presentinvention; however, the invention is not intended to be limited to theseexamples. Parts are by weight unless otherwise indicated.

Example 1 A printing paste is prepared by milling parts of2,2,4,4'-tetrahydroxybenzophenone into 40 parts of linseed oil until ahomogeneous paste is obtained. This paste is then used on a two rollofl-set printing press and anodized aluminum is printed in the usualmanner. Then, the printed aluminum is heated at 110 C. for minutes toremove the vehicle and the color is fixed onto the metal surface byimmersing it in boiling water for 15 minutes. The colored metal isremoved and dried. It has a green-yellow color which exhibits excellentlight fastness.

Example 2 Example 1 is repeated using 2,2'dihydroxy-4,4-dimethoxybenzophenone in a vehicle of linseed oil. Thedyed aluminum is colored green-yellow and exhibits excellent lightfastness.

Example 3 Example 1 is repeated using 2,2',4,4'-tetrahydroxy-5,5'-di-tert.butyl-benzophenone. The aluminum is colored green-yellow andexhibits excellent light fastness.

Example 4 When 4,6dibenzoyl resorcinol is used as colorant in theprocess of Example 1, a green-yellow dyed aluminum is obtained.

Example 5 (a) One part of 5 tert.butyl 2,2,4 trihydroxybenzophenone isdissolved in 1 part of dimethylformamide and the solution is stirredinto 3 parts of silk screen base (a solution of nitrocellulose in methylethyl ketone). The resulting paste is brushed onto a piece of freshlyanodized aluminum (0.8 mil oxide coating), and the aluminum article isheated at 110 C. for minutes. The piece of aluminum is then immersed inboiling water for 30 minutes. The surface of the colored aluminum iscleaned by rinsing with dimethylformamide, then with acetone. Thegreen-yellow coloration thus obtained exhibits excellent light fastness.

Similar results are obtained when the 5-tert.butyl-2,2,4-trihydroxybenzophenone employed in this example is replaced by anequal amount of any of the following colorants: 5,5 di-tert.butyl2,2,4,4 tetrahydroxybenzophenone, 2,2 dihydroxy 4,4dimethoxybenzophenone, 2,2',4,4 tetrahydroxybenzophenone, 2,2,4-trihydroxybenzophenone and 2,2-dihydroxy-4-methoxy-4-ethoxybenzophenone.

(b) When 1 part of 2,3,4-trihydroxybenzophenone (Alizarin Yellow A) isemployed as the colorant in part (a) of this example, one obtains agreen-yellow coloration having extremely poor light fastness.

Example 6 One part of 5-tert.butyl-2,2',4-trihydroxybenzophenone isdissolved in 65 parts of dimethyl-formamide. A strip of anodizedaluminum (0.8 mil oxide coating) is immersed in said solution for 5minutes. The strip is removed from the solution, heated at 110 C. for 20minutes and then immersed in boiling water for 30 minutes. The aluminumarticle is cleaned by rinsing with dimethylformamide, then with acetone.A light-fast, green-yellow coloration is obtained.

The amount of solvent employed in this example may be varied from 20parts to 100 parts per part of colorant, depending on the depth of shadedesired.

Other solvents may be substituted for the dimethylformamide, e.g.diethylformamide, dimethylacetarnide, diethylacetamide anddimethylsulfoxide, giving similar results.

As many widely different embodiments of this invention may be madewithout departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:

1. In the process of coloring oxide-coated aluminum With a non-aqueousink so as to impart a light-fast, greenyellow color thereto, the stepwhich comprises applying to said oxide-coated aluminum an ink comprisinga non-aqueous vehicle and a coloring agent contained therein, saidcoloring agent being an o-hydroxybenzophenone of the formula R OH I O III o wherein R is selected from the group consisting of hydrogen and ahydroxy radical; X is selected from the group consisting of hydrogen, ahydroxy radical and a lower alkoxy radical; X is selected from the groupconsisting of hydrogen and a lower alkyl radical; each Y isindependently selected from the group consisting of hydrogen, a tertiarylower alkyl radical and an acyl radical, RCO, wherein R is selected fromthe group consisting of a lower alkyl radical and a phenyl radical.

2. The process of claim 1 wherein the coloring agent is5-tert.butyl-2,2',4-trihydroxybenzophenone.

3. The process of claim 1 wherein the coloring agent is2,2',4,4'-tetrahydroxybenzophenone.

4. The process of claim 1 wherein the coloring agent is2,2'-dihydroxy-4,4-dimethoxybenzophenone.

5. The process of claim 1 wherein the coloring agent is2,2'-dihydroxy-4-methoxy-4-ethoxybenzophenone.

6. The process of claim 1 wherein the coloring agent is 4,6-dibenzoylresorcinol.

7. Green-yellow colored oxide-coated aluminum containing on the surfacethereof a coating of an aluminum chelate of an o-hydroxybenzophenone ofthe formula wherein R is selected from the group consisting of hydrogenand a hydroxy radical; X is selected from the group consisting ofhydrogen, a hydroxy radical and a lower alkoxy radical; X is selectedfrom the group consisting of hydrogen and a lower alkyl radical; each Yis independently selected from the group consisting of hydrogen, atertiary lower alkyl radical and an acyl radical, RCO, wherein R isselected from the group consisting of a lower alkyl radical and a phenylradical.

8. In the process of coloring oxide-coated aluminum with a non-aqueousink so as to impart a light-fast, green yellow color thereto, the stepwhich comprises printing on said oxide-coated aluminum an ink comprisinga nonaqueous vehicle and a coloring agent contained therein, saidcoloring agent being an o-hydroxybenzophenone of the formula wherein Ris selected from the group consisting of hydrogen and a hydroxy radical;X is selected from the References Cited in the file of this patent groupconsisting of hydrogen, a hydroxy radical and 2. UNITED STATES PATENTSlower al koxy radical; X is selected from the group consisting ofhydrogen and a lower alkyl radical; each Y 160mg 2 i 1 is independentlyselected firom the group consisting of 5 2250473 i er 3 3 hydrogen, atertiary lower alkyl radical and an acyl radi- 576 3 y 1957 cal, ROO--,wherein R is selected from the group con- 2927872 f f m 3;; 1960 slstmgof a lower alkyl rachcal and a phenyl radical. 1, 3 43 Dessauer Jam 196210 3,066,054 McNamara Nov. 27, 1962 OTHER REFERENCES Organic Chemistry,Furon and Snyder, pp. 68 and 69'. Copyright 1942. Copy on Examinersdesk.

1. IN THE PROCESS OF COLORING OXIDE-COATED ALUMINUM WITH A NON-AQUEOUS INK SO AS TO IMPART A LIGHT-FAST, GREENYELLOW COLOR THERETO, THE STEP WHICH COMPRISES APPLYING TO SAID OXIDE-COATED ALUMINUM AN INK COMPRISING A NON-AQUEOUS VEHICLE AND A COLORING AGENT CONTAINED THEREIN, SAID COLORING AGENT BEING AN O-HYDROXYBENZOPHENONE OF THE FORMULA 